1. Field of the Invention
The present invention is generally related to the field of baseball and softball and more specifically to a baseball or softball bat.
2. Description of the Related Art
High performance baseball and softball bats, hereinafter referred to simply as “baseball bats” or “bats”, are primarily made from aluminum alloys, composite materials, or some combination thereof. These bats are tubular (hollow inside) so as to optimize their weight and they consist of three sections: a relatively narrow handle portion for gripping, a relatively wider distal portion for hitting, and a tapered mid-section connecting the handle and hitting portions. Original aluminum bats were fabricated as a single piece in that they solely consisted of a frame with nothing occupying the space within the frame. It was found that these bats outperformed traditional wooden bats because of a “rebound” effect present in aluminum/composite bats. As the ball impacted the bat, the bat wall would absorb the energy from the impact by elastically deforming the wall at the point of impact. As the ball began to leave the bat the energy absorbed by the elastic deformation would be released by the wall returning to its original structure, in effect giving the ball an extra “push”, thus the rebound effect. Another name given to this effect is the “trampoline” effect. Manufacturers of bats found that by making the wall thinner the rebound effect would be magnified. However thinner walls also decreased the life of the bat as the wall would fatigue and no longer return to its original position; leaving dents or dings on the bat. As a result manufacturers begin to look at ways of utilizing the cavity within the hitting portion of the bat to increase the rebound effect and reduce fatigue.
A number of designs were introduced to take advantage of the space available in the cavity of the bat's hitting portion with the goal of strengthening the hitting portion while maintaining or improving the rebound effect. Some designs would decrease the width of the cavity so as to add an outer tubular sleeve while other designs would add tubular inserts within the cavity of the bat's hitting portion. These designs became to be known as multi-walled bats. Still other designs added composites to the outer wall or disks within the cavity to strengthen the wall while maintaining its flexing properties. These designs continued to be known as single wall bats. As this disclosure is for a bat with a novel method of utilizing a tubular insert this discussion will focus on multiwall bat disclosures.
Multiwall bat designs may be broken down into two groups. The first group have walls that are distinct from each other yet each wall directly and continuously adjoins adjacent walls. Although the walls may flex independently from each other the fact that they adjoin one another only allows for minor improvements to the rebound effect. The second group have walls where a gap(s) between the walls have been purposefully incorporated. The gap(s) allow for greater independent flexing of the walls with a corresponding greater improvement of the rebound effect so that the rebound effect may increase more linearly.
Examples of bats with multiple walls that directly abuts one another include U.S. Pat. No. 5,303,917 to Uke and U.S. Pat. No. 6,440,017 to Anderson which both discloses a bat with a sleeve over the outside of the hitting portion that directly and continuously adjoins the frame of the bat's hitting portion. Examples of bats with internal walls, referred to as inserts, includes U.S. Pat. No. 5,364,095 to Easton which discloses an internal insert bonded to the inside of the external metal tube and running the full length of the hitting portion of the bat and U.S. Pat. No. 6,425,836 to Misono et al. which discloses an internal insert with a weak boundary layer so as to encourage some amount of independent flexing. The advantage of these designs is simplicity in manufacturing. Since the walls directly and continuously adjoin each other they are less likely to separate. However this simplicity comes at a cost to performance as less energy is absorbed from the ball's impact with the bat resulting in a less than desired rebound effect.
Examples of bats with multiple walls that incorporate some sort of gap between the walls include U.S. Pat. No. 5,414,398 to Eggiman which discloses a bat with a tubular insert that is placed within the bat's hitting portion. The outside diameter of the insert is smaller than the inside diameter of the bat's outer shell so that there exists an annular gap between the two. The outside shell and tubular insert are therefore able to flex independently and, by so doing, together act as a leaf spring, resulting in greater bat performance. To prevent the insert from moving about within the frame it is secured by friction fit or fasteners. Another example is U.S. Pat. No. 6,612,945, also to Anderson, that contains a spiral inspired textured insert that makes contact with the bat's frame at each apex of the spiral. While the two walls are not as independent as the Eggiman patent they do act with greater independence than walls that directly and continuously adjoin one another. The spiral inspired textured insert is seated against a buttress at one end of the hitting portion and secured by the bat's end cap at the opposite end of the hitting portion. A final example is U.S. Pat. No. 8,007,381 to Watari et al. which discloses a bat with sleeve that fits over the outside of the hitting portion with an inside diameter larger than the outside diameter of the bat's frame such that a gap exists between the two. The sleeve is secured to the bat's frame by both structural elements and adhesives at both ends of the sleeve. The walls in multiwall bats that contain gaps between the walls are able to absorb more energy from an impact with a ball as they are able to flex with greater independence from each other. The increase in flexing in turn improve the bat's rebound effect and performance.
However all of the designs presented here are, in essence, single wall designs as the separate walls are securely connected or make contact, either continuously or at two or more points, with each other. As a result energy absorbed by the bat is transmitted to each wall at multiple points, not just the point of impact. Additionally the walls, since they are connected to each other, freely allow energy absorbed as vibrations to travel along the full length of the bat's frame and every structural element attached to the bat's frame.
On impact with a ball a bat absorbs energy by two means; flexing and vibrating. Energy that flexes the wall leads to improved rebound effect. In the multiwall designs presented here the walls will flex at each point they are in contact with each other. Using the Eggiman patent as an example the inner wall will flex at the two points where it is secured to the outer wall and where the ball impacts with the outer wall. Although most of the energy that flexes the inner wall will be at the point of impact some flexing energy will “bleed away” at the other two points where the inner wall is secured to the outer wall and correspondingly reduce the amount of flexing at the point of impact. When a ball impacts a bat the bat will vibrate. Although the bat will always vibrate the amount of vibrations may sometimes be felt by the batter and can lead to the batter experiencing a “stinging” sensation in their hands. Energy absorbed as vibrations adversely affects the rebound effect in two ways. First it can be easily seen that vibration energy directly subtracts from flexing energy in that the more energy absorbed by vibration the less energy is available to be absorbed for flexing. Vibrations also adversely impact the rebound effect by actively working against the wall flexing. Vibrations are an oscillatory effect creating an equal amount of movement away from a resting point. As the wall is flexed energy will have to be expended to overcome the vibrations resulting in a reduction of the energy used to flex the wall and therefore a less than optimal rebound effect.
The prior art designs presented herein provide for a less than optimal rebound effect by means of the multiple points of contact between the walls and the multiple points of contact allow vibrations to spread throughout the bat.